Wet-formed composite defining latent voids and macro-cavities

ABSTRACT

A wet-formed composite defining latent voids and macro-cavities, the wet-formed composite having a basis weight greater than about 100 grams per square meter and a density of about 0.06 grams per cubic centimeter or more. The wet-formed composite comprises fibers and superabsorbent material, with the superabsorbent material present in an amount of about 10 dry weight percent or less, specifically about 5 dry weight percent or less, and particularly about 2 dry weight percent or less, but more than 0, based on the total dry weight of fibers and superabsorbent material present in the wet-formed composite. By virtue of the superabsorbent material having been allowed to swell and then shrink during the making of the wet-formed composite, macro-cavities are created. Densification compresses the macro-cavities. The resulting composite expands upon wetting and exhibits good absorbency properties.

[0001] This application is a divisional of parent U.S. patentapplication Ser. No. 09/643,803, filed on Aug. 22, 2000. The parentapplication claims priority from U.S. Provisional Application No.60/150,325 filed on Aug. 23, 1999.

BACKGROUND

[0002] People rely on absorbent products, including diapers, femininepads, dressings for wounds, and adult incontinence articles, toparticipate in and enjoy their daily activities.

[0003] Absorbent products are generally manufactured by combiningseveral components. For disposable absorbent products that are worn by auser, these components typically include a liquid-permeable topsheet; aliquid-impermeable backsheet attached to the topsheet; and an absorbentstructure located between the topsheet and the backsheet. When thedisposable product is worn, the liquid-permeable topsheet is positionednext to the body of the wearer and allows passage of bodily fluids intothe absorbent structure. The liquid-impermeable backsheet helps preventleakage of fluids held in the absorbent structure. Ideally the absorbentstructure has three features: (1) it quickly wicks fluid into thestructure; (2) it distributes fluid throughout the structure; and (3) itretains a lot of fluid.

[0004] These features can be difficult to simultaneously incorporateinto the same structure. Absorption capacity increases when internalvoid volume in an absorbent structure increases. A higher void volumeallows for containment of larger amounts of fluid. Furthermore, anabsorbent structure with a higher void volume can better holdmultiphasic-fluids containing solids; e.g., menses or feces.

[0005] But a higher internal void volume can mean larger pore diametersand a reduced ability to wick fluid into and throughout the absorbentstructure.

[0006] What is needed is an absorbent structure, and a method of makingthis structure, that provide both a high absorbent capacity and theability to wick fluid into and throughout the absorbent structure.

SUMMARY

[0007] The present invention is directed to an absorbent structure, anda method of making the absorbent structure, that satisfy this need. Onemethod of making a wet-formed composite having latent voids andmacro-cavities comprises providing fibers, a dispersion medium for thefibers, and a superabsorbent material swellable in the dispersionmedium, the superaborbent material present in an amount of about 10 dryweight percent or less, specifically about 5 dry weight percent or less,and particularly about 2 dry weight percent or less, but more than 0,based on the total dry weight of fibers and superabsorbent materialpresent in the wet-formed composite; thereafter combining the fibers,superabsorbent material, and dispersion medium; forming a wet-formedcomposite comprising fibers and superabsorbent material, and definingvoids between the fibers, from the combination comprising fibers,superabsorbent material, and dispersion medium; providing sufficientcontact time between the superabsorbent material and dispersion mediumso that the superabsorbent material swells prior to drying thewet-formed composite; drying the wet-formed composite so that thesuperabsorbent material shrinks, thereby forming macro-cavities betweenthe fibers; and densifying the wet-formed composite to collapse thevoids and macro-cavities, thereby forming latent voids andmacro-cavities within the densified wet-formed composite; wherein thedensified wet-formed composite has a density of about 0.06 grams percubic centimeter or greater and a basis weight greater than about 100grams per square meter.

[0008] In its dry state, a wet-formed composite of the present inventionis suitable for wicking fluids into and throughout the composite. Whenthe wet-formed composite is insulted with fluid, that portion of thecomposite that is wetted expands as the superabsorbent material swellsand latent voids and macro-cavities manifest themselves. This expansionincreases internal void volume and absorbent capacity. The portion ofthe structure that is not yet wetted, i.e. the structure at and beyondthe fluid front, remains in its unexpanded form, and therefore suitablefor wicking fluids into and throughout portions of the compositeincreasingly remote from the initial point of fluid insult.

[0009] In another aspect, a method of the present invention comprisesproviding sufficient contact time between the superabsorbent materialand dispersion medium before drying the wet-formed composite such thatthe superabsorbent material swells to at least about 50% of its maximumabsorbent capacity, particularly to at least about 75% of its maximumabsorbent capacity, specifically to at least about 90% of its maximumabsorbent capacity, and more specifically to at least about 95% of itsmaximum absorbent capacity prior to drying the wet-formed composite. Forpapermaking processes used to make a wet-formed composite of the presentinvention, the dispersion medium will generally be a source of waterused to operate the papermaking equipment (e.g., city/municipalwater—treated or untreated at the papermaking site, papermaking processwater, and the like).

[0010] In still another aspect, a method of the present inventioncomprises providing sufficient contact time between the superabsorbentmaterial and dispersion medium before drying the wet-formed compositesuch that the superabsorbent material swells by at least about 20 grams,specifically at least about 50 grams, more specifically at least about75 grams, particularly at least about 100 grams, more particularly atleast about 150 grams, and still more particularly at least about 300grams of dispersion medium per gram of superabsorbent material.

[0011] In yet another aspect, the amount of dispersion medium retainedin the superabsorbent material after drying is suitably less than about10% of the superabsorbent material's maximum absorbent capacity,particularly less than about 5% of the material's maximum absorbentcapacity, specifically less than about 2% of the material's maximumabsorbent capacity, and more specifically less than about 1% of thematerial's maximum absorbent capacity.

[0012] Other methods of the present invention further comprise the useof materials such as resilient fibers, synthetic fibers, wet-strengthagents, dry-strength agents, other additives, and the like, in processesfor preparing a wet-formed composite.

[0013] In another aspect, methods of the present invention may comprisehydroentangling the newly formed wet-formed composite (i.e., the nascentweb).

[0014] Another method of the present invention involves making adisposable absorbent article, the method comprising providing aliquid-permeable topsheet, a liquid-impermeable backsheet, and awet-formed composite defining latent voids and macro-cavities;positioning the wet-formed composite so that it will lie between thetopsheet and the backsheet in the disposable absorbent article; anddirectly or indirectly attaching at least a portion of the topsheet toat least a portion of the backsheet.

[0015] Furthermore, the present invention encompasses combining awet-formed composite having latent voids and macro-cavities with otherabsorbent structures (e.g., an airlaid structure or the like) to form anabsorbent core (e.g., a multi-layer absorbent core comprising thewet-laid composite and the airlaid structure). Alternatively, more thanone wet-formed composite of the present invention may be combined toform a multi-layered absorbent core, with each of the plurality ofwet-formed composites having the same or different materials and/orproperties. Furthermore, a wet-formed composite defining latent voidsand macro-cavities may be combined with films, nonwoven webs, and thelike to form a multi-layered structure or laminate.

[0016] An absorbent structure having features of the present inventioncomprises a wet-formed composite having interbonded fibers that definelatent voids and macro-cavities between the fibers; and superabsorbentmaterial contained by the interbonded fibers, the superabsorbentmaterial present in an amount of about 10 dry weight percent or less,specifically about 5 dry weight percent or less, and particularly about2 dry weight percent or less, but more than 0, based on the total dryweight of fibers and superabsorbent material present in the wet-formedcomposite. Wet-formed composites of the present invention have a densityof about 0.06 grams per cubic centimeter or greater and a basis weightgreater than about 100 grams per square meter.

[0017] Wet-formed composites of the present invention may furthercomprise materials such as resilient fibers; synthetic fibers; wet- ordry-strength agents; other additives; and the like.

[0018] In another aspect, wet-formed composites of the present inventionare characterized by certain functional properties having recited valuesor ranges. Examples of such properties include wet:dry cohesivestrength, dry internal-cohesion, intake time, Gurley-type stiffness,wicking velocity, and increases in caliper upon wetting (theseproperties are discussed below).

[0019] The present invention also encompasses disposable absorbentarticles comprising a wet-formed composite defining latent voids andmacro-cavities.

[0020] These and other features, aspects, advantages, and versions ofthe present invention will become better understood with regard to thefollowing description, appended claims, and accompanying drawings.

DRAWINGS

[0021]FIG. 1 depicts one version of a paper machine capable of makingone or more embodiments of the present invention.

[0022]FIG. 2 depicts one version of a paper machine capable of makingone or more embodiments of the present invention.

[0023]FIG. 3 depicts the relationship between intake time, in seconds,and fiber composition, in weight percent, for different embodiments ofthe present invention.

[0024]FIG. 4 depicts the relationship between wicking distance, incentimeters, and time, in minutes, for different embodiments of thepresent invention.

[0025]FIG. 5 depicts the relationship between capacity, in grams pergram, and distance from the initial point of fluid insult, in inches,for different embodiments of the present invention.

[0026]FIG. 6 depicts the relationship between fluid retained, in grams,and pledget length, in inches, for different embodiments of the presentinvention.

[0027]FIG. 7 depicts the relationship between fluid capacity, in gramsper gram at a pressure of 0.5 pounds-force per square inch (psi), andfiber composition, in weight percent, for different embodiments of thepresent invention.

DESCRIPTION/REPRESENTATIVE EMBODIMENTS

[0028] Reference now will be made to representative embodiments of thepresent invention, including examples set forth below. Each embodimentand example is provided by way of explanation. It will be apparent toone skilled in the art that various modifications and variations can bemade without departing from the scope or spirit of the invention.

[0029] One process for preparing a wet-formed composite defining latentvoids and macro-cavities comprises the steps of: providing fibers, adispersion medium for the fibers, and a superabsorbent materialswellable in the dispersion medium, the superabsorbent material presentin an amount of about 10 dry weight percent or less, specifically about5 dry weight percent or less, and particularly about 2 dry weightpercent or less, but more than 0, based on the total dry weight offibers and superabsorbent material present in the wet-formed composite;thereafter combining the fibers, superabsorbent material, and dispersionmedium; forming a wet-formed composite, comprising fibers andsuperabsorbent material, and defining voids between the fibers, from thecombination of fibers, superabsorbent material, and dispersion medium;providing sufficient contact time between the superabsorbent materialand dispersion medium so that the superabsorbent material swells priorto drying the wet-formed composite; drying the wet-formed composite sothat the superabsorbent material shrinks, thereby forming macro-cavitiesbetween the fibers; and densifying the wet-formed composite to collapsethe voids and macro-cavities, thereby forming latent voids andmacro-cavities within the densified wet-formed composite; wherein thedensified wet-formed composite has a density of about 0.06 grams percubic centimeter or greater and a basis weight greater than about 100grams per square meter.

[0030] Other versions of a process of the present invention aredescribed herein. Presently representative materials useful for thepresent invention are discussed.

[0031] Fibers suitable for use in the present invention are known tothose skilled in the art. Any fiber from which a wet-formed compositecan be formed is believed suitable for use. Examples of fibers suitablefor use in the present invention include, cellulosic fibers such as woodpulp, cotton linters, cotton fibers and the like; synthetic polymericfibers such as polyolefin fibers, polyamide fibers, polyester fibers,polyvinyl alcohol fibers, polyvinyl acetate fibers, synthetic polyolefinwood pulp fibers, and the like; as well as regenerated cellulose fiberssuch as rayon and cellulose acetate microfibers. Mixtures of variousfiber types are also suitable for use. For example, a mixture ofcellulosic fibers and synthetic polymeric fibers may be used. As ageneral rule, the fibers will have a length-to-diameter ratio of atleast about 2:1, preferably of at least about 5:1. As used herein,“diameter” refers to a true diameter if generally circular fibers areused or to a maximum transverse cross-sectional dimension ifnon-circular, e.g., ribbon-like, fibers are used. The fibers willgenerally have a length of from about 0.5 millimeter to about 25millimeters, preferably from about 1 millimeter to about 6 millimeters.Fiber diameters will generally be from about 0.001 millimeter to about1.0 millimeter, preferably from about 0.005 millimeter to about 0.01millimeter. For reasons such as economy, availability, physicalproperties, and ease of handling, cellulosic wood pulp fibers aresuitable for use in the present invention.

[0032] Other fibers useful for purposes of the present invention areresilient fibers that include high-yield pulp fibers (further discussedbelow), flax, milkweed, abaca, hemp, cotton, or any of the like that arenaturally resilient or any wood pulp fibers that are chemically orphysically modified, e.g. crosslinked or curled, that have thecapability to recover after deformation from preparing the composite, asopposed to non-resilient fibers which remain deformed and do not recoverafter preparing the composite.

[0033] As used herein, “high yield pulp fibers” are those papermakingfibers produced by pulping processes providing a yield of about 65percent or greater, more specifically about 75 percent or greater, andstill more specifically from about 75 to about 95 percent. Such pulpingprocesses include bleached chemithermomechanical pulp (BCTMP),chemithermomechanical pulp (CTMP), pressure/pressure thermomechanicalpulp (PTMP), thermomechanical pulp (TMP), thermomechanical chemical pulp(TMCP), high yield sulphite pulps, and high yield kraft pulps, all ofwhich leave the resulting fibers with higher levels of lignin. Suitablehigh-yield pulp fibers are generally characterized as being comprised ofcomparatively whole, relatively undamaged tracheids, high freeness (over250 CSF), and low fines content (less than 25 percent by the Britt jartest).

[0034] The amount of resilient fibers in the wet-formed composite can beat least about 10 dry weight percent or greater, more specifically about30 dry weight percent or greater, still more specifically about 50 dryweight percent or greater, particularly about 70 dry weight percent orgreater, and up to 100 dry weight percent based on the total dry weightof fibers present in the wet-formed composite. For layered wet-formedcomposites, i.e. composites made using a stratified or multi-layeredheadbox, these same amounts can be applied to one or more of theindividual layers. Individual layers may have the same or differentamounts of resilient fibers.

[0035] As used herein, the term “superabsorbent material” and similarterms refer to a water-swellable, generally water-insoluble materialcapable of absorbing at least about 20, specifically at least about 50,more specifically at least about 75, particularly at least about 100,more particularly at least about 150 times, and still more particularlyat least about 300 times or more its weight in water (or otherdispersion medium). The superabsorbent material may be formed fromorganic material which may include natural materials such as agar,pectin, and guar gum, as well as synthetic materials such as synthetichydrogel polymers. Synthetic hydrogel polymers include, for example,carboxymethylcellulose, alkali metal salts of polyacrylic acid and itscopolymers, polyacrylamides, polyvinyl alcohol, ethylene maleicanhydride copolymers, polyvinyl ethers, hydroxypropylcellulose,hydroxypropyl acrylate, polyvinyl morpholinone, polymers and copolymersof vinyl sulfonic acid, polyacrylates, polyacrylamides, polyvinylpyridine, and the like. Other suitable polymers include hydrolyzedacrylonitrile grafted starch, acrylic acid grafted starch, andisobutylene maleic anhydride copolymers and mixtures thereof. Thehydrogel polymers are suitably lightly crosslinked to render thematerial substantially water-insoluble. Crosslinking may, for example,be by irradiation or by covalent, ionic, Van der Waals, or hydrogenbonding. Suitable materials are available from various commercialvendors, such as the Dow Chemical Company, Stockhausen Inc., andChemtall Inc. The noncellulosic, synthetic hydrogel polymers aresuitable for use in the present invention.

[0036] The superabsorbent material may be in the form of discreteparticles, agglomerated particles, fibers, spheres or the like. When inthe form of discrete particles, the particles will generally have amaximum cross-sectional dimension of from about 10 micrometers to about2000 micrometers, specifically of from about 50 micrometers to about1000 micrometers, and more specifically from about 100 micrometers to500 micrometers.

[0037] The superabsorbent material present in the wet-formed compositesis swellable in the dispersion medium. As used herein, a superabsorbentmaterial will be considered to be swellable in the dispersion mediumwhen the superabsorbent material can absorb at least about 20 times,specifically at least about 50 times, more specifically at least about75 times, particularly at least about 100 times, more particularly atleast about 150 times, and still more particularly at least about 300times or more its weight in the dispersion medium when thesuperabsorbent material is dispersed in an excess of the dispersionmedium for a period of one hour.

[0038] A variety of materials may be suitable for use as the dispersionmedium. Exemplary of dispersion mediums are water, other aqueousmaterials, and the like. For reasons such as availability and economy,water is a suitable dispersion medium. For papermaking processes used tomake wet-formed composites of the present invention, the dispersionmedium may be city/municipal water, papermaking process water, treatedwater, or some other source of water used in operating the papermakingequipment (e.g., the stock preparation system; discussed in more detailbelow).

[0039] Prior to the fiber/dispersion medium slurry (and other elementsthat may be present in the slurry; e.g. superabsorbent material and/orother additives as detailed herein) being conducted to a forming surfaceto form a nascent web (i.e., a newly formed wet-formed composite), thefibers are present in the dispersion medium in an amount of from about0.005 to about 3.0 weight percent, specifically of from about 0.01 toabout 2.0 weight percent and, particularly from about 0.01 to about 1.0weight percent, based on total weight of the fibers and dispersionmedium (known to those skilled in the art as “consistency”). Thedispersion medium may contain other additives known to those skilled inthe art of papermaking. Other suitable additives include, withoutlimitation, binders, viscosity modifiers, adhesives, dry-strengthagents, wet-strength agents (discussed in more detail below), pH controladditives, flocculants, and the like, provided they do not deleteriouslyaffect the formation or desired performance properties of the wet-formedcomposites. Additives may also be combined with the wet-formed compositeafter the composite has been formed (e.g., by spraying, coating,printing, or the like).

[0040] There are a number of materials commonly used in the paperindustry to impart wet strength to paper and board that are applicableto this invention. These materials are known in the art as wet-strengthagents and are commercially available from a wide variety of sources.Any material that when added to a wet-formed composite increases the wetcohesive strength:dry cohesive strength ratio in excess of 0.05 will,for purposes of this invention, be termed a wet-strength agent.Typically these materials are termed either as permanent wet-strengthagents or as “temporary” wet-strength agents. For the purposes ofdifferentiating permanent from temporary wet strength, permanent will bedefined as those resins which, when incorporated into wet-formedcomposites, will provide a composite that retains more than 50% of itsoriginal wet-cohesive strength after exposure to water for a period ofat least five minutes. Temporary wet-strength agents are those that showless than 50% of their original wet cohesive strength after exposure towater for five minutes. Both classes of material find application in thepresent invention.

[0041] The amount of wet-strength agent added to the pulp fibers can beat least about 0.1 dry weight percent or greater, specifically at leastabout 0.2 dry weight percent or greater, particularly at least about 0.5dry weight percent or greater, more particularly from about 0.2 to about1 dry weight percent, and still more particularly from about 0.1 toabout 3 dry weight percent based on the dry weight of the fibers.

[0042] The permanent wet-strength agents that are of utility in thepresent invention are typically water soluble, cationic, oligomeric orpolymeric resins that are capable of either crosslinking with themselves(homocrosslinking) or with the cellulose or other constituent of thefiber. The most widely used materials for this purpose are the class ofpolymer known as polyamide-polyamine-epichlorohydrin (PAE) type resins.These materials have been described in patents issued to Keim (U.S. Pat.Nos. 3,700,623 and 3,772,076) and are sold by Hercules, Inc.,Wilmington, Del., as Kymene 557H. Related materials are marketed byHenkel Chemical Co., Charlotte, N.C. and Georgia-Pacific Resins, Inc.,Atlanta, Ga.

[0043] Polyamide-epichlorohydrin resins are also useful as bondingresins in this invention. Materials developed by Monsanto and marketedunder the Santo Res label are base-activated polyamide-epichlorohydrinresins that can be used in the present invention. These materials aredescribed in patents issued to Petrovich (U.S. Pat. No. 3,855,158; U.S.3,899,388; U.S. 4,129,528 and U.S. 4,147,586) and van Eenam (U.S.4,222,921). Although they are not as commonly used in consumer products,polyethylenimine resins are also suitable for immobilizing the bondpoints in the products of this invention. Other classes ofpermanent-type wet-strength agents are exemplified by the aminoplastresins obtained by reaction of formaldehyde with melamine or urea.

[0044] The temporary wet-strength resins that can be used in connectionwith this invention include, but are not limited to, those resins thathave been developed by American Cyanamid and are marketed under the nameParez 631 NC (now available from Cytec Industries, West Paterson, N.J.).This and similar resins are described in U.S. Pat. Nos. 3,556,932 toCoscia et al. and 3,556,933 to Williams et al. Other temporarywet-strength agents that should find application in this inventioninclude modified starches such as those available from National Starchand marketed as Co-Bond 1000. It is believed that these and relatedstarches are covered by U.S. Pat. No. 4,675,394 to Solarek et al.Derivatized dialdehyde starches, such as described in Japanese KokaiTokkyo Koho JP 03,185,197, should also find application as usefulmaterials for providing temporary wet strength. It is also expected thatother temporary wet-strength materials such as those described in U.S.Pat. No. 4,981,557, U.S. 5,008,344, and U.S. 5,085,736 to Bjorkquistwould be of use in this invention. With respect to the classes and thetypes of wet-strength resins listed, it should be understood that thislisting is simply to provide examples and that this is neither meant toexclude other types of wet-strength resins, nor is it meant to limit thescope of this invention.

[0045] Although wet-strength agents as described above find particularadvantage for use in connection with this invention, other types ofbonding agents can also be used. They can be applied at the wet end orapplied by spraying or printing, etc. after the wet-formed composite isformed or after it is dried.

[0046] As used herein, the wet:dry ratio is the ratio of the wetcohesive strength divided by the dry cohesive strength. Cohesivestrength, as used herein, means z-directional bonding strength. Cohesivestrength is measured by mounting a sample between sample holders on atensile tester. Two-sided adhesive tape is used on the surface of eachholder so that the opposing faces of the sample are each affixed to asample-holder surface. The tensional forces act on opposing faces of thesample, thus providing a measure of z-directional bonding strength.Wet-formed composites of the present invention that comprise awet-strength agent will have a wet:dry ratio of about 0.05 or greater,more specifically about 0.1 or greater, still more specifically about0.15 or greater, particularly about 0.3 or greater, still moreparticularly about 0.5 or greater, and still more particularly about 0.7or greater.

[0047] As used herein, the terms “wet-formed,” “wet-laid,” and the likerefer to composites that are formed from a process in which fibers aredispersed in a liquid dispersion medium to form a slurry. The slurry isdeposited on a forming surface to form the composite by removal of atleast a portion of the dispersion medium. Those skilled in the art arefamiliar with such processes.

[0048]FIG. 1 depicts one version of a paper machine capable of making anembodiment of the invention. For simplicity, the various tensioningrolls schematically used to define the several fabric runs are shown butnot numbered. It will be appreciated that variations from the apparatusand method illustrated in FIG. 1 can be made without departing from thescope of the invention.

[0049] A slurry of fibers and the dispersion medium is prepared in astock preparation system (not shown). Such systems are known to personsof ordinary skill. The superabsorbent material is combined with theslurry of fibers so that the superabsorbent material absorbs at leastabout 20 times, specifically at least about 50 times, more specificallyat least about 75 times, particularly at least about 100 times, moreparticularly at least about 150 times, and still more particularly atleast about 300 times or more its weight in the dispersion medium beforethe wet-formed composite is dried. Suitably the superabsorbent materialswells to the above-recited amounts before the wet-formed composite isformed. The superabsorbent material may be added at a location in thestock preparation system so that the superabsorbent material isdistributed relatively uniformly throughout the slurry prior to forminga wet-formed composite. The superabsorbent material may also bepreswollen in a dispersion medium, suitably the same or similardispersion medium as is used to prepare the fiber slurry, before beingadded to the fiber slurry. If a multi-layer or stratified headbox isused, differing amounts, chemistries, types, or shapes of superabsorbentmaterial may be added to each stock preparation system used to feed agiven layer in the headbox.

[0050] The maximum amount of dispersion medium which the superabsorbentmaterial absorbs, after being combined with the slurry of fibers anddispersion medium until the point of drying, can be experimentallydetermined by comparing the weight of the wet composite, prior todrying, to the weight of the dry composite after drying. The weight ofdispersion medium removed by drying generally represents the maximumamount of dispersion medium capable of being absorbed by thesuperabsorbent material. Such a calculation assumes all dispersionmedium removed by drying was present in the superabsorbent material. Theactual amount of dispersion medium held in the superabsorbent materialprior to drying is less than the experimentally-determined maximumamount (some of the dispersion medium may be in or between fibers butnot in the superabsorbent material) and depends on the length ofexposure of the superabsorbent material to the dispersion medium, aswell as the relative amounts of fiber and superabsorbent material in thewet-formed composites.

[0051] Returning to FIG. 1, the diagram depicts a twin-wire formerhaving a layered papermaking headbox 10 which injects or deposits astream 11 of the fiber/dispersion medium/superabsorbent materialcombination onto the forming fabric 13 which serves to support and carrythe newly-formed wet-formed composite (i.e., the nascent web) in theprocess as the composite is partially dewatered to a consistency ofabout 10 dry weight percent. Additional dewatering of the wet-formedcomposite can be carried out, such as by vacuum suction, while thecomposite is supported by the forming fabric.

[0052] A person of ordinary skill will recognize that one or all layersof the stratified headbox may be devoted to preparing a wet-formedcomposite of the present invention. Furthermore, each layer may containdiffering amounts, chemistries, types, or shapes of superabsorbentmaterial or resilient fibers, as well as differing amounts, chemistries,or types of wet-strength agents or other additives, so that each layerhas different performance characteristics. Alternatively, a single-layerheadbox may be employed to make wet-formed composites encompassed by thepresent invention.

[0053] The wet-formed composite is then transferred from the formingfabric to a transfer fabric 17. The transfer fabric may travel at aslower speed than the forming fabric in order to impart increasedstretch into the composite. Transfer is suitably carried out with theassistance of a vacuum shoe 18 such that the forming fabric and thetransfer fabric converge and diverge simultaneously at the leading edgeof the vacuum slot as described in U.S. Pat. No. 5,667,636 to Engel etal., which is hereby incorporated by reference in a manner consistentherewith.

[0054] The wet-formed composite is then transferred from the transferfabric to the through-air-drying fabric 19 with the aid of a vacuumtransfer roll 20 or a vacuum transfer shoe, optionally again using afixed-gap transfer as previously described. Alternatively, thewet-formed composite may be transferred directly from the forming fabricto the through-air-drying fabric. The through-air-drying fabric can betraveling at about the same speed or a different speed relative to thetransfer fabric or forming fabric. If desired, the through-air-dryingfabric can be run at a slower speed to further enhance stretch. Transferis suitably carried out with vacuum assistance to ensure deformation ofthe sheet to conform to the through-air-drying fabric, thus yieldingdesired bulk and appearance. Suitable through-air-drying fabrics includethose having a three-dimensional contour as described in U.S. Pat. No.5,429,686 issued Jul. 4, 1995 to Chiu et al. entitled “Apparatus ForMaking Soft Tissue Products”, which is hereby incorporated by reference.

[0055] The level of vacuum used for the wet-formed composite transferscan be from about 3 to about 15 inches of mercury (75 to about 380millimeters of mercury), suitably about 5 inches (125 millimeters) ofmercury. The vacuum shoe (negative pressure) can be supplemented orreplaced by the use of positive pressure from the opposite side of thewet-formed composite to blow the wet-formed composite onto the nextfabric in addition to or as a replacement for sucking it onto the nextfabric with vacuum. Also, a vacuum roll or rolls can be used to replacethe vacuum shoe(s).

[0056] While supported by the through-air-drying fabric, the wet-formedcomposite is final dried to a consistency of about 80 percent or greaterby the through-air-dryer 21 and thereafter transferred to a carrierfabric 22. The dried composite 23 is transported to the reel 24 usingcarrier fabric 22 and an optional carrier fabric 25. An optionalpressurized turning roll 26 can be used to facilitate transfer of thewet-formed composite from carrier fabric 22 to fabric 25. Suitablecarrier fabrics for this purpose are Albany International 84M or 94M andAsten 959 or 937, all of which are relatively smooth fabrics having afine pattern.

[0057] Densification of the wet-formed composite can be carried out by anumber of methods. It is well known that passing sheets through one ormore rollers or nips will help compress and smooth the surfaces ofmaterials. The equipment used to do this is termed a calender orsupercalender. The effect of calendering on composites of the presentinvention depends upon the temperature, the pressure applied, and theduration of the pressure. For purposes herein, calendering can becarried out at either at ambient or elevated temperatures. Suitablecalendering pressures can be from about 50 to about 1400 pounds-forceper linear inch (pli). Suitable temperatures can be from about 20° C. toabout 240° C. The duration of calendering can be varied in conjunctionwith the nip pressure to produce the desired caliper for the sheet.

[0058] In addition to calendering or supercalendering, the wet-formedcomposites can be densified using flat platten presses or fabric nipsused to smooth and compact multi-wiper products as disclosed in U.S.Pat. No. 5,399,412 to Sudall et al. In this instance, the multi-plywiper is carried on fabrics through a nip and the overall caliper of themulti-ply product is reduced. A similar process can be used to producecomposites of the present invention. By inducing a pattern in the fabricor fabrics, the resulting composite could have areas that are highlycompressed and areas that are less compressed. The response of theresulting composites to fluids would result in expansion of thecomposite, more or less uniformly, for the entire composite.

[0059] In some versions of the invention, the nascent web of fibers(i.e., the newly-formed wet-formed composite) is hydroentangled usingequipment known to those skilled in the art. For example, U.S. Pat. No.6,022,818, entitled “Hydroentangled Nonwoven Composites,” which ishereby incorporated by reference in a manner consistent with the presentapplication, describes one version of a hydroentangling process (see,e.g., col. 8, lines 4-64 for one description of such a process). Asdescribed in the Examples below, hydroentangling affects cohesion andstiffness of the resulting composite. Generally, increasinghydroentangling of the fibers in a nascent web increases cohesivestrength and decreases stiffness in the dried, wet-formed composite.Furthermore, increasing hydroentangling of the nascent web typicallyincreases the dryness of the web just after the hydroentanglingoperation. Accordingly, positioning a hydroentangling unit operationbefore the selected drying operation (whether it be a through-air-dryingoperation; a Yankee dryer; a series of drying cans; an irradiativedrying operation; some combination of these; or some other operationused to increase the percent solids of the web—i.e., reduce the amountof moisture in the web) would be expected to decrease the amount ofenergy required by the selected drying operation to achieve a givenpercent solids in the web after the drying operation.

[0060] The schematic in FIG. 2 shows one version of a process comprisingan example of hydraulic entangling equipment. As discussed above, aslurry comprising fibers and the selected dispersion medium is preparedin a stock preparation system (not shown). The slurry is supplied to aheadbox 112 and is deposited via a sluice 114 onto a forming surface116. One example of a forming surface is a Formtech 90BH Flat Warp 90×50mesh, single-layer weave, available from Albany International ofPortland, Tenn. The warp strands are 0.17 mm polyester. The shutestrands are 0.25 mm polyamide. The average caliper is 0.018 inch; AirPermeability is 525 cfm (cubic feet per minute); and the open area is 20percent. The slurry may be diluted to any consistency that is typicallyused in a conventional papermaking process. For example, the slurry maycontain from about 0.05 to about 0.5 percent by weight pulp fibers inwater to form a slurry. The slurry is deposited on the forming surface116 and a vacuum assist 117 is used to pull water out of the depositedfibers thereby creating a newly-formed wet-formed composite 118 (i.e., anascent web of fibers).

[0061] The wet-formed composite 118 is then directed to a foraminousentangling surface 132 of a hydraulic entangling machine. The wet-formedcomposite 118 passes under one or more hydraulic entangling manifolds134 and is treated with jets of fluid to entangle the pulp fibers withone another, thereby forming a hydroentangled wet-formed composite 136.Alternatively, hydraulic entangling may take place while the wet-formedcomposite 118 is on the same foraminous screen (i.e., mesh fabric) onwhich wet-laying took place. The present invention also contemplatesrehydrating a dried, wet-formed composite to a specified consistency andthen subjecting the rehydrated wet-formed composite to hydraulicentangling. The hydraulic entangling may take place while the wet-formedcomposite 118 is highly saturated with water. For example, thewet-formed composite 118 may contain up to about 90 percent by weightwater just before hydraulic entangling.

[0062] The hydraulic entangling may be accomplished utilizing hydraulicentangling equipment such as may be found in, for example, U.S. Pat. No.3,485,706 to Evans and U.S. Pat. No. 5,284,703 to Everhart et al, bothof which are incorporated herein by reference in their entirety and in amanner consistent herewith. The hydraulic entangling may be carried outwith any appropriate working fluid such as, for example, water. Theworking fluid flows through one or more manifolds 135 which evenlydistribute the fluid to a series of individual holes or orifices. Theholes or orifices may be from about 0.003 to about 0.015 inches (0.076to 0.38 millimeters) in diameter. For example, the invention may bepracticed utilizing a manifold produced by Honeycomb Systems, Inc. ofBiddeford, Me. containing a single row of aligned holes (30 holes perinch/12 holes per centimeter) with each hole having a diameter of 0.007inches (0.18 millimeters). In the process used to form the examples ofthe present invention, three manifolds of the type just described werealigned in sequence across the traveling layers 118 and 120. In thehydraulic entangling process the working fluid passes through theorifices at a pressure ranging from about 200 to about 2000 pounds persquare inch gauge (psig) (about 1379 kilopascals to about 13,790kilopascals). The number of manifolds 135 and the pressure within eachmanifold will affect the degree of integration of the fibers.

[0063] The fluid impacts the wet-formed composite 118 which is supportedby a foraminous surface 132 which may be, for example, a single planemesh wire having a mesh size of from about 40×40 strands per inch(15.7×15.7 strands per centimeter) to about 100×100 strands per inch(39.4×39.4 strands per centimeter). The foraminous surface 132 may alsobe a multi-ply mesh having a mesh size from about 50×50 to about 200×200strands per inch (19.7×19.7 to about 78.7×78.7 strands per centimeter).One example of a foraminous surface used in the hydraulic entanglingoperation may be obtained from Albany International of Portland, Tenn.The wire may be described as a 12-C Flat Warp 14×15 mesh, single-layerweave. The warp strands are 0.88×0.57 mm polyester. The shute strandsare 0.76 mm polyamide. The average caliper is 0.0515 inch; airpermeability is 770 cfm (cubic feet per minute); and the open area is 28percent.

[0064] As is typical in many water-jet treatment processes, vacuum slots138 may be located directly beneath the hydro-needling manifolds 135 orbeneath the foraminous entangling surface 132 downstream of themanifolds 135 so that excess water can be withdrawn from the entangledwet-formed composite 136.

[0065] After the fluid jet treatment, the entangled wet-formed composite136 may be transferred to a non-compressive drying operation or acompressive drying operation such as steam cans (not shown). Adifferential speed pick-up roll 140 may be used to transfer the materialfrom the hydraulic needling belt to a non-compressive drying operation.Alternatively, conventional vacuum-type pick-ups and transfer fabricsmay be used. If desired, the composite fabric may be wet creped beforebeing transferred to the drying operation. Non-compressive drying of theweb may be accomplished utilizing a conventional rotary drum through-airdryer 142. The through-air dryer 142 maybe an outer rotatable cylinder144 with perforations 146 in combination with an outer hood 148 forreceiving hot air blown through the perforations 146. A through-dryerbelt 150 carries the composite fabric 136 over the upper portion of thethrough-dryer outer cylinder 144. The heated air forced through theperforations 146 in the outer cylinder 144 of the through-dryer 142removes water from the entangled wet-formed composite 136. Thetemperature of the air forced through the composite fabric 136 by thethrough-dryer 142 may range from about 93 degrees Celsius (C.) to about260 degrees C. (200 degrees F. to about 500 degrees F.). Other usefulthrough-drying methods and apparatus may be found in, for example, U.S.Pat. Nos. 2,666,369 and 3,821,068, both of which are incorporated hereinby reference in their entirety and in a manner consistent herewith.

[0066] As discussed above, finishing steps and/or post-treatmentprocesses may be used to impart selected properties to the entangledwet-formed composite 136. For example, the composite may be pressed bycalendar rolls, and/or creped or brushed to provide a uniform exteriorappearance and/or certain tactile properties. Alternatively, and/oradditionally, chemical post-treatments such as surfactants, adhesives ordyes may be added to the entangled wet-formed composite.

[0067] The dried wet-formed composites of the present invention comprisefibers in an amount of about 90 dry weight percent or greater,specifically about 95 dry weight percent or greater, and particularly ofabout 98 dry weight percent or greater, but less than 100 dry weightpercent, based on total dry weight of the fibers and superabsorbentmaterial present in the wet-formed composite. The fibers areinterbonded, either through fiber-fiber interactions or by the effect ofone or more additives such as a wet-strength agent, and these bonds maybe covalent, ionic, of the Van der Waals type, of the hydrogen-bondtype, or some combination of these.

[0068] The superabsorbent material is present in an amount of about 10dry weight percent or less, specifically of about 5 dry weight percentor less, and particularly of about 2 dry weight percent or less, butmore than 0, based on the total dry weight of the fibers andsuperabsorbent material present in the wet-formed composite. The amountof superabsorbent material is selected in part so that the wet-formedcomposite comprises interbonded fibers defining macro-cavities betweenthe fibers after the drying step, but does not significantly reduceproduction capacity by virtue of the amount of water that must beremoved from the swollen superabsorbent material during the drying step.

[0069] Suitably the superabsorbent material swells to at least about 50%of its maximum absorbent capacity, particularly to at least about 75% ofits maximum absorbent capacity, specifically to at least about 90% ofits maximum absorbent capacity, and more specifically to at least about95% of its maximum absorbent capacity prior to the step in which thewet-formed composite is dried. For purposes of this application,“maximum absorbent capacity” means the amount of dispersion medium(e.g., city/municipal water; papermaking process water; or other liquid)absorbed and/or adsorbed by the superabsorbent material when thesuperabsorbent material is placed in an excess of the dispersion mediumfor a time sufficient for the superabsorbent material to swell to itsmaximum capacity (i.e., it is no longer absorbing and/or adsorbingdispersion medium), which generally will be achieved after one hour atroom temperature (i.e., from about 68 to about 72 degrees Fahrenheit).Many superabsorbent materials will achieve their maximum absorbentcapacity in a time less than one hour. Thus a superabsorbent materialwith a maximum absorbent capacity of 150 grams of dispersion medium pergram of superabsorbent material is fully swollen and is at 100% of thematerial's absorbent capacity when 1 gram of the superabsorbent materialhas absorbed/adsorbed 150 grams of dispersion medium. It should beunderstood that other measures of maximum absorbent capacity may beused, with the invention encompassing wet-formed composites comprising asuperabsorbent material that is appreciably swollen (i.e., thesuperabsorbent material is at about 50% to about 75% of its maximumabsorbent capacity), particularly substantially swollen (i.e., thesuperabsorbent material is at about 75% to about 95% of its maximumabsorbent capacity), and more particularly fully swollen before thewet-formed composite is dried (i.e., the superabsorbent material is atabout 95% to about 100% of its absorbent capacity). Increasing thedegree of swelling prior to the drying step should increase the size ofthe latent macrocavities because a more fully-swollen superabsorbentshould occupy more volume in the wet-formed composite prior to drying.But a more fully-swollen superabsorbent material may mean thatadditional water must be driven off during drying (depending on thedegree to which the fully-swollen superabsorbent material issubsequently shrunk). The amount of dispersion medium retained in thesuperabsorbent material after drying is suitably less than about 10% ofthe material's maximum absorbent capacity, particularly less than about5% of the material's maximum absorbent capacity, specifically less thanabout 2% of the material's maximum absorbent capacity, and morespecifically less than about 1% of the material's maximum absorbentcapacity.

[0070] Dried wet-formed composites of the present invention have a basisweight less than about 600 grams per square meter, specifically lessthan about 250 grams per square meter, more specifically less than about150 grams per square meter, particularly between about 150 and about 250grams per square meter, but more than about 100 grams per square meter.

[0071] After the dried wet-formed composite has been densified,composites of the present invention have a density of about 0.06 gramsper cubic centimeter or greater, specifically of about 0.12 grams percubic centimeter or greater, more specifically of about 0.15 grams percubic centimeter or greater, and particularly from about 0.12 to about0.15 grams per cubic centimeter, but less than about 0.5 grams per cubiccentimeter. Density is selected in part so that the internal porestructure of the dried, wet-formed composite is suitable for wicking anddistributing fluid throughout the composite. Density may also beselected so that the dried, wet-formed composite helps impart softnessand thinness to the product in which the wet-formed composite isincorporated.

[0072] When fully wetted or saturated with dispersion medium (e.g.,city/municipal water), the caliper of the wet-formed composite of thisinvention can increase by about 50 percent or greater, specifically byabout 100 percent or greater, more specifically by about 200 percent orgreater, still more specifically by about 400 percent or greater,particularly from about 400 percent to about 600 percent, and moreparticularly by about 600 percent or greater.

[0073] Dried wet-formed composites of the present invention are suitablefor incorporation into a number of types of absorbent articles. Forexample, wet-formed composites defining latent voids and macrocavitiesmay be used as, or part of, an absorbent core in articles such asfeminine care articles, dressings for wounds, diapers,adult-incontinence articles, and the like. Furthermore, the presentinvention contemplates combining a wet-formed composite having latentvoids and macro-cavities with other absorbent structures (e.g., anairlaid structure or the like) to form an absorbent core (e.g., amulti-layer absorbent core comprising the wet-laid composite and theairlaid structure). Alternatively, more than one wet-formed compositemay be combined to form a multi-layered absorbent core, with each of theplurality of wet-formed composites having the same or differentproperties. Furthermore, a wet-formed composite defining latent voidsand macro-cavities may be combined with films, nonwoven webs, and thelike.

[0074] Examples of disposable absorbent articles or absorbent compositesinto which wet-formed composites of the present invention may beincorporated include, but are not limited to: U.S. Pat. No. 4,940,464,entitled “Disposable Incontinence Garment or Training Pant,”; U.S. Pat.No. 5,904,675, entitled “Absorbent Article with Improved Elastic Marginsand Containment System,”; U.S. Pat. No. 5,904,672, entitled “AbsorbentArticle having Improved Waist Region Dryness and Method ofManufacture,”; U.S. Pat. No. 5,902,297, entitled “Absorbent ArticleHaving a Collection Conduit,”; U.S. Pat. No. 4,372,312, entitled“Absorbent Pad Including Microfibrous Web”; and U.S. Pat. No. 4,770,657,entitled “Three-Dimensional Shaped Feminine Pad with Absorbent in theElasticized Edges”; each of which is hereby incorporated by reference inits entirety in a manner consistent herewith.

[0075] These variations are given only as examples. It should beunderstood, however, that the invention encompasses use of wet-formedcomposites defining latent voids and macrocavities in other combinationsand in other absorbent articles or composites.

[0076] To illustrate the invention, representative embodiments ofwet-formed composites of the present invention were made and tested asdiscussed below.

EXAMPLE 1

[0077] Some embodiments of the wet-formed composites were made using aModel Number Series 9000 computerized handsheet former, manufactured byM/K Systems, Danvers, Mass. The general procedure for making theseembodiments was as follows. First, the selected amount of fiber wasdispersed in water along with the selected amount of Kymene 557LX,available from Hercules Inc., a business having offices in Wilmington,Del., to form a slurry of fibers. Next the slurry of fibers was added tothe mold of the handsheet former. The slurry was agitated by dispersingair into the slurry for about 60 seconds. The selected amount ofsuperabsorbent material, after having been placed in distilled water(approximately 1000 g distilled water for 1 g of superabsorbentmaterial) for about 15 to 30 minutes, was then added to the slurry inthe mold and agitation with air continued for about 60 seconds. Theagitation was then stopped, and the slurry/superabsorbent materialcombination allowed to stand for about 5 seconds. Water was drained fromthe mold to form a wet-formed composite on the screen. Two blotters wereplaced on the composite and a roller was used to contact the compositewith the blotters. The wet-formed composite was then picked up andplaced onto a stainless steel wire screen and dried in a convection ovenat 105 degrees Celsius. After drying, the sheet was densified to achievethe desired caliper for a given basis weight. The densifying device usedfor these examples was a Model 3912 hydraulic press available from FredS. Carver Hydraulic Equipment Inc., a business having offices inMenomonee Falls, Wis. Dried handsheets, or samples cut from rolls (seeExamples 8 and 9 below), were placed on a bottom plate. The device wasthen activated so that the upper plate was hydraulically pressed againstthe sample and lower plate. The applied pressure typically was about16,000 pounds per square inch.

EXAMPLE 2

[0078] The fluid handling properties of wet-formed composites made inaccordance with the procedures outlined in Example 1 were measured usinga low viscosity menses simulant (see U.S. Pat. No. 5,883,231, entitled“Artificial Menses Fluid,” which is incorporated by reference, forrecipes of such simulants). For this example, and the examples thatfollow, the simulant comprised 30% swine red blood cells; 30% swineblood plasma; and 40% bird egg white. Intake times were measured byinsulting 0.25 ml of simulant for each insult, at a flow rate of 5ml/hour, to the surface of a 1-inch by 6-inch sample of the wet-formedcomposite, and recording the elapsed time at which the applied volume ofsimulant was no longer detectable visually at the surface of the sample.Three insults were done at the same point to get the intake time foreach insult. The results depicted in FIG. 3 are the average of 3 datapoints. The wet-formed composites used in the test had a basis weight of600 grams per square meter and contained 5% by dry weight superabsorbentmaterial (Flosorb 60 Lady from Chemtall Inc., Riceboro, Ga). Thesuperabsorbent had a maximum absorbent capacity of about 300-350 gramsof dispersion medium per gram of superabsorbent material. For thisexample, the dispersion medium was city/municipal water. Thesuperabsorbent material was fully swollen, i.e. the superabsorbentmaterial was at about 95 to about 100% of its maximum absorbentcapacity, before the drying step. A calendering device was used todensify the wet-formed composites to a density of 0.3 grams per cubiccentimeter and a caliper of 0.217 cm prior to testing. The slurry offibers comprised various blends of a predominantly bleached, softwoodkraft pulp such as CR54 or CR1654 (Alliance Corp.) and NHB416, acrosslinked, resilient fiber from Weyerhaeuser, a business havingoffices in Federal Way, Washington. Kymene 557LX was added at a level of0.5 dry weight percent. Superabsorbent material, preswollen as describedin Example 1 above, contacted water for about 60 seconds in the moldwhile making the handsheet. FIG. 3 depicts results of intake time versusvarying content of the resilient fiber (NHB416). The results also showthat intake time can be adjusted to the desired value by varying thefiber blend.

EXAMPLE 3

[0079] The fluid distribution properties of wet-formed compositesprepared as described in Example 1, and having the characteristics ofcomposites used in Example 2, were evaluated using a horizontal wickingtest. The test was conducted by applying 5 ml of simulant at the rate of5 ml/hour using a syringe pump to the center of 1-inch by 6-inch stripsof the wet-formed composites. (Note: because of differences in how thesimulant was applied between Example 2 and Example 3—i.e., multipleinsults versus the continuous delivery of simulant, the rate of decreaseof density and the rate of increase in caliper differed between the twoexamples.) The distance wicked as a function of time was monitored andrecorded, with the results depicted in FIG. 4. The distance wicked wasmeasured by determining the total length of the stain, from one end tothe other end along the 6-inch dimension of the sample, as the simulantwas wicked into and through the wet-formed composite. For each of thefiber blends evaluated, FIG. 3 shows that wicking distance increasedwith time, indicating that fluid was efficiently wicked away from thepoint of insult. The data indicate that the simulant was wicked from thepoint of insult at a wicking velocity of about 1.5 mm min⁻¹ (i.e., theapproximate slope of a straight line fitting the points).

EXAMPLE 4

[0080] The distribution of fluid in wet-formed composites prepared asdescribed in Example 3 was measured as a function of distance from thepoint of insult. Samples that had been used to determine wickingdistance as described in Example 3 were sectioned so that each sectioncorresponded to a given distance from the initial point of insult.Capacity, in grams per gram, was measured for each section. FIG. 5depicts the results of this test.

EXAMPLE 5

[0081] A test that measures the combination of desorption anddistribution of simulant by the wet-formed composites prepared asdescribed in Example 1 was conducted by placing a 175 gram per squaremeter airlaid material (comprising 10% by weight thermoplastic binderfiber T-255, Hoescht-Celanese, and 90% by weight fluff pulp NB416,Weyerhaeuser; the airlaid material having a density of 0.08 gram percubic centimeter) over a 600 gram per square meter wet-formed compositehaving a density of 0.3 grams per cubic centimeter and containing 5% bydry weight Flosorb 60 Lady superabsorbent material. The fiber furnishfor the wet-formed composite was a blend of 30% NHB 416 and 70%predominantly bleached, softwood kraft pulp, such as CR54 or CR1654.Kymene 557LX was added at a level of 0.5 dry weight percent. A 1-inch by5-inch strip of the airlaid material was placed on the 1-inch by 5-inchstrip of the wet-formed composite and simulant applied to the airlaidstrip at a rate of 12 ml/hour using a syringe pump for 45 minutes. Atthe end of the test the two strips were separated and the fluiddistribution in both layers was determined. The results shown in FIG. 7show the ability of the wet-formed composite to desorb fluid from theairlaid material and distribute/retain the fluid.

EXAMPLE 6

[0082] The ability of wet-formed composites prepared as described inExample 1, and having the characteristics of composites used in Example2, to retain the simulant was measured by allowing a 1.5-inch by1.5-inch sample of the wet-formed composite to swell in 20 millilitersof simulant in a weight dish for 30 minutes. The sample was then removedfrom the weight dish and free fluid allowed to drip for 5 seconds. Thesample was then placed between two blotter paper sheets (3-inch by3-inch blotter) and placed between a bladder. The sample between the twoblotter paper sheets was then exposed to a pressure of 0.5 pounds-forceper square inch (psi) for 30 seconds. The sample was then removed andweighed to determine the absorption capacity under 0.5 psi pressure. Theresults of retention capacity of the wet-formed composites under 0.5 psipressure are depicted in FIG. 7.

EXAMPLE 7

[0083] Wet-formed composites were prepared and immersed in simulant asdescribed in Example 6. But instead of determining the retentioncapacity under pressure, the caliper of these wetted wet-formedcomposites was determined. Upon being wetted with simulant as describedin Example 6, the caliper of the wet-formed composite increased to 0.64cm. Prior to being wetted the wet-formed composite had a caliper of0.217 cm. Prior to densification, the wet-formed composite had a caliperof 0.665 cm. Thus the caliper of the densified wet-formed compositeincreased by 195% upon wetting. Caliper was measured under a pressure of0.05 psig using a Starret-type bulk tester (described below).

EXAMPLE 8

[0084] The process generally depicted in FIG. 2 and described above wasused to make wet-formed composites. In one case the composite washydraulically entangled. In a second case the composite was nothydraulically entangled. The forming surface (i.e., a Formtech 90BH FlatWarp 90×50 mesh, single-layer weave, available from Albany Internationalof Portland, Tenn.) and hydraulic-entangling surface (i.e., a 12-C FlatWarp 14×15 mesh, single-layer weave, available from Albany Internationalof Portland, Tenn.) identified above were used to make examples of thepresent invention. For these examples, the line speed of the papermakingmachine was between 9 and 15 feet per minute. The through-air dryertemperature was set to approximately 400 degrees Fahrenheit. The pulpslurry used to make the wet-formed composite was made up by mixing 26 lbof NHB 416, a crosslinked, resilient southern softwood fiber availablefrom Weyerhaeuser, a business having offices in Federal Way, Washington;54 lb of CR1654, a southern softwood/hardwood blend available from U.S.Alliance, a business having offices in Coosa, Ala.; in 7642 gallons(i.e., about 63,800 lb) of water. The resulting pulp slurry had aconsistency of about 0.125%. After the slurry had been madesubstantially uniform through the action of a mixer, 1.6 lb of apolyacrylate superabsorbent material available under the tradedesignation Flosorb 60 Lady was added to the pulp slurry in the stockchest. This amount of superabsorbent material corresponded to about 2dry weight percent, based on total dry weight of the fibers andsuperabsorbent material present in the wet-formed composite.

[0085] The polyacrylate superabsorbent was swellable in the chosendispersion medium (i.e., water). The superabsorbent material was mixedwith the fiber/water slurry for at least about 15 minutes beforeactivating a pump (not shown) to conduct the fiber/superabsorbent/waterslurry to the headbox and onto the forming surface. The superabsorbentmaterial was estimated to have absorbed at least about 300 times itsweight in the dispersion medium (i.e., water) before the pump wasactivated. In other words, the superabsorbent material, Flosorb 60 Ladyswelled to at least about 85-100% of its maximum absorbent capacitybefore the pump was activated.

[0086] For wet-formed composite that was not hydroentangled, thehydraulic jets were not activated. The foraminous surface passed throughthe unactivated hydraulic entangling equipment, thereby conducting thewet-formed composite from the forming section to the non-compressivedrying section, in this case a through-air drier.

[0087] The dried roll of wet-formed composite was later used as a sourceof smaller samples that were densified as described in Example 1 (i.e.,using a Carver-type hydraulic press). The densified wet-formed compositewas tested for basis weight, caliper, cohesion, and Gurley Stiffness.The methods by which these characteristics were measured are describedbelow.

[0088] A hydraulically entangled wet-formed composite was made in thesame way as the composite described in the preceding paragraphs, but inthis case the hydraulic entangling equipment was activated. For thisexample, the jets were operated at a gauge pressure of 600 psig. Thespecifications for the equipment are generally given above in thedescription of the process depicted in FIG. 2. Three manifolds producedby Honeycomb Systems, Inc. of Biddeford, Me. were used. Each manifoldcontained a single row of aligned holes (30 holes per inch/12 holes percentimeter) with each hole having a diameter of 0.007 inches (0.18millimeters).

[0089] After drying, the samples from the roll ofhydraulically-entangled composite were densified as described above(again using the Carver-type hydraulic press). The hydraulicallyentangled wet-formed composite was then tested for basis weight,caliper, cohesion, and Gurley Stiffness.

[0090] Table 1 presents a comparison of the physical properties of ahydraulically entangled wet-formed composite (i.e., a wet-formedcomposite with HET) and a wet-formed composite that was nothydraulically entangled (i.e., a wet-formed composite without HET).TABLE 1 Basis MD Gurley CD Gurley Weight Caliper Cohesion StiffnessStiffness [g m⁻²] [mm] [kg_(f)] [mg_(f)] [mg_(f)] Wet-formed 212 1.852.02 2131 1834 composite without HET Wet-formed 202 1.94 5.77 1343  462composite with HET

[0091] The data shows that the hydraulically-entangled wet-formedcomposite has greater cohesion, and is less stiff, than a wet-formedcomposite that is not hydraulically entangled.

[0092] The above physical characteristics were measured in the followingmanner. For basis weight, a sample having an area of no less than 20 in²was placed on a calibrated balance. After the weight of the sample wasmeasured, basis weight was calculated by dividing the weight of thesample by the area of the sample. For this example, the basis weight wasdetermined in an unconditioned room having a temperature of about 68 toabout 72 degrees Fahrenheit and a relative humidity of about 60%.

[0093] Caliper is a measure of thickness and was measured at 0.05 psiwith a Starret-type bulk tester, in units of millimeters. The foot ofthe bulk tester used in these studies was a small acrylic cylindermeasuring about 3 inches wide by about 0.5 inches in thickness.

[0094] Internal Cohesion was measured in the following manner. A 2×2inch sample of material to be tested was adhered with double-sidedadhesive to a 2×2 inch metal platen (#1) to which was attached a piston.A fixed, flat platen (#2) is rotated into position above the platen #1and the platen #1 is pressed against the platen #2 for 3 seconds tosecure the sample to the platen #1. The platen #2 is then rotated out ofthe test area. A 1×1 inch platen (#3) having a piece of double-sidedadhesive mounted thereon is rotated into position above the platen #1and the platen #1 is raised and pressed against the platen #3 for 10seconds, adhering the sample to the two pieces of double-sided adhesive.The platen #1 is then slowly lowered. A digital force gauge, model DFI50(available from S. A. Meier Co., Milwaukee, Wis.) is mounted on top ofthe platen #3. The gauge measures the peak load in kilograms needed tototally separate the sample from the double-sided adhesive. Anotherdescription of the internal cohesion test is given in U.S. Pat. No.5,964,973 to Heath et al. beginning at line 59 in column 14, which ishereby incorporated by reference in a manner consistent herewith. Forthe test results reported in Table 1, the internal cohesion values arereported for dry samples, hence the values represent dry internalcohesion values.

[0095] For purposes of the present invention, the various rigiditystiffness values are determined with respect to a bending momentproduced by a force that is directed perpendicular to the planesubstantially defined by the length and width of the component beingtested. A suitable technique for determining the rigidity, stiffnessvalues described herein is a Gurley Stiffness test, a description ofwhich is set forth in TAPPI Standard Test T 543pm-84 (Stiffness of paper(Gurley type stiffness tester)). A suitable testing apparatus is aGurley Digital Stiffness Tester; Model 4171-D manufactured by TeledyneGurley (514 Fulton Street, Troy, N.Y. 12181-0088). This instrumentallows the testing of a wide variety of materials through the use ofvarious lengths and widths in combination with the use of a 5, 25, 50,or 200 gram weight placed in one of three positions on the pointer ofthe apparatus. For purposes of the present description, the statedGurley stiffness values are intended to correspond to the values thatwould be generated by a “standard” sized sample. Accordingly, the scalereadings from the Gurley stiffness tester are appropriately converted tothe stiffness of a standard size sample and are expressed in terms ofmilligrams. The standard size sample has a width of 1″ and a nominallength of 3″ (actual length of 3.5″). The actual length of the sample isthe nominal length, plus an additional 0.25″ of length for holding inthe clamp and another 0.25″ of length for overlapping the vane. Tablesof factors for taking scale readings generated with non-standard sizedtest samples and converting the readings to the stiffness of thestandard size sample are given in the Instruction Manual for the GurleyStiffness Tester provided by Teledyne Gurley. Accordingly, otherdesignated dimensions for the test sample may also be convenientlyemployed, so long as the appropriate conversion factor is employed todetermine the appropriate value which corresponds to the standard sizesample.

EXAMPLE 9

[0096] The process generally depicted in FIG. 2 and described (seeExample 8) was used to make wet-formed composites. In two cases thecomposite was hydraulically entangled at a gauge pressure of either 600psig or 1000 psig. In a third case the composite was not hydraulicallyentangled. The forming surface and hydraulic-entangling surfaceidentified above were used to make examples of the present invention.For these examples, the line speed of the papermaking machine was 9 feetper minute. The through-air dryer temperature was set to approximately400 degrees Fahrenheit. The pulp slurry used to make the wet-formedcomposite was made up by mixing 26 lb of NHB 416, a resilient,crosslinked southern softwood fiber available from Weyerhaeuser, abusiness having offices in Federal Way, Washington; 54 lb of CR1654, asouthern softwood/hardwood blend available from U.S. Alliance, abusiness having offices in Coosa, Ala.; in 63,800 lb of water. Theresulting pulp slurry had a consistency of about 0.125%. After theslurry had been made substantially uniform through the action of amixer, 1.6 lb of a polyacrylate superabsorbent material available underthe trade designation Flosorb 60 Lady was added to the pulp slurry inthe stock chest. This amount of superabsorbent material corresponded to2 dry weight percent, based on total dry weight of the fibers andsuperabsorbent material present in the wet-formed composite.

[0097] The polyacrylate superabsorbent was swellable in the chosendispersion medium (i.e., water). The superabsorbent material was mixedwith the fiber/water slurry for at least about 15 minutes beforeactivating a pump (not shown) to conduct the fiber/superabsorbent/waterslurry to the headbox and onto the forming surface. The superabsorbentmaterial was estimated to have absorbed at least about 300 times itsweight in the dispersion medium (i.e., water) before the pump wasactivated.

[0098] For wet-formed composite that was not hydroentangled, thehydraulic jets were not activated. The foraminous surface passed throughthe unactivated hydraulic entangling equipment, thereby conducting thewet-formed composite from the forming section to the non-compressivedrying section, in this case a through-air drier.

[0099] After passing through unactivated hydroentangling equipment, thedryness (i.e., the percent solids) of the wet-formed composite wasdetermined.

[0100] A hydraulically entangled wet-formed composite was made in thesame way as the composite described in the preceding paragraphs, buthere the hydraulic entangling equipment was activated. For this example,the hydraulic entangling equipment comprised three manifolds produced byHoneycomb Systems, Inc. of Biddeford, Me., each manifold containing asingle row of aligned holes (30 holes per inch/12 holes per centimeter)with each hole having a diameter of 0.007 inches (0.18 millimeters). Thejets were operated at a gauge pressure of either 600 psig or 1000 psig.

[0101] After passing through activated hydroentangling equipment, thedryness (i.e., the percent solids) of the wet-formed composite wasdetermined.

[0102] Table 2 presents a comparison of the dryness (i.e., percentsolids) of the wet-formed composite with and without hydraulicentangling of the composite's constituent fibers. TABLE 2Hydroentangling? No Yes Yes HET Gauge Pressure 0 600 1000 [psig] Dryness[% solids] 20.6 26.5 35.5

[0103] As can be seen from Table 2, activation of the hydraulicentangling equipment increased the dryness of the wet-formed composite.Furthermore, increasing the gauge pressure of the jets whilehydroentangling increased the dryness of the hydroentangled wet-formedcomposite.

[0104] Although the present invention has been described in considerabledetail with reference to certain versions, other versions are possible.The spirit and scope of the appended claims should not be limited to thedescription of specific versions contained herein.

What is claimed is:
 1. A disposable absorbent article, comprising aliquid-permeable topsheet; a liquid-impermeable backsheet; and anabsorbent core disposed between the topsheet and the backsheet; theabsorbent core comprising a wet-formed composite which includes:interbonded fibers defining a plurality of latent voids andmacro-cavities between the fibers, the fibers including at least about10% by weight resilient fibers; and superabsorbent material contained bythe interbonded fibers, the superabsorbent material present in an amountof less than about 5 dry weight percent, but more than 0, based on thetotal dry weight of the fibers and superabsorbent material.
 2. Thedisposable absorbent article of claim 1, wherein the wet-formedcomposite has a density of at least 0.06 grams per cubic centimeter. 3.The disposable absorbent article of claim 1, wherein the wet-formedcomposite has a basis weight greater than about 100 grams per squaremeter.
 4. The disposable absorbent article of claim 1, wherein theresilient fibers are selected from high-yield pulp fibers, flax,milkweed, abaca, hemp, cofton, crosslinked pulp fibers, curled pulpfibers, and combinations thereof.
 5. The disposable absorbent article ofclaim 1, wherein the wet-formed composite includes superabsorbentmaterial in an amount of about 2 dry weight percent or less, but morethan zero, based on the total weight of superabsorbent material andfibers.
 6. The disposable absorbent article of claim 1, wherein thewet-formed composite further comprises a wet-strength additive.
 7. Thedisposable absorbent article of claim 1, wherein the fibers in thewet-formed composite include at least about 30% by weight resilientfibers.
 8. The disposable absorbent article of claim 1, wherein thefibers in the wet-formed composite include at least about 50% by weightresilient fibers.
 9. The disposable absorbent article of claim 1,wherein fibers in the wet-formed composite include at least about 70% byweight resilient fibers.
 10. A disposable absorbent article, comprisinga liquid-permeable topsheet; a liquid-impermeable backsheet; and anabsorbent core disposed between the topsheet and the backsheet; theabsorbent core comprising a wet-formed composite having latent voids andmacro-cavities, which includes: interbonded fibers including resilientfibers and a wet strength additive; and a superabsorbent materialcontained by the interbonded fibers; the wet-formed composite having awet:dry cohesive strength ratio of about 0.1 or greater, a dry internalcohesion value greater than about 5 kg, a cross-directional Gurley-typestiffness value less than about 500 mg, a density of about 0.06 gramsper cubic centimeter or greater, and a basis weight greater than about100 grams per square meter.
 11. The disposable absorbent article ofclaim 10, wherein the wet-formed composite has a wet:dry cohesivestrength ratio of about 0.15 or greater.
 12. The disposable absorbentarticle of claim 10, wherein the wet-formed composite has a wet:drycohesive strength ratio of about 0.30 or greater.
 13. The disposableabsorbent article of claim 10, wherein the wet-formed composite has awet:dry cohesive strength ratio of about 0.50 or greater.
 14. Thedisposable absorbent article of claim 10, wherein the wet-formedcomposite has a wet:dry cohesive strength ratio of about 0.70 orgreater.
 15. A disposable absorbent article comprising a wet-formedcomposite having latent voids and macro-cavities, the wet-formedcomposite including: interbonded fibers defining a plurality of latentvoids and macro-cavities between the fibers, the fibers including atleast about 10% by weight resilient fibers; and superabsorbent materialcontained by the interbonded fibers, the superabsorbent material beingpresent in an amount of less than about 5 dry weight percent, but morethan zero, based on the total dry weight of the fibers andsuperabsorbent material.
 16. The disposable absorbent article of claim15, comprising a feminine care article.
 17. The disposable absorbentarticle of claim 15, comprising a wound dressing.
 18. The disposableabsorbent article of claim 15, comprising a diaper.
 19. The disposableabsorbent article of claim 15, comprising an adult incontinence article.20. The disposable absorbent article of claim 15, wherein the resilientfibers are selected from high yield pulp fibers, flax, milkweed, abaca,hemp, cotton, crosslinked pulp fibers, curled pulp fibers, andcombinations thereof.
 21. The disposable absorbent article of claim 15,wherein the wet-formed composite further comprises a wet strengthadditive.